Various types of clamping devices for cylindrical workpieces exist, which are sometimes also known as clamp chucks. Some, which are manual, include an operating handwheel; others of the automatic type include a system which effects automatic displacement of the clamping jaws or chaps towards the work-piece (tube or bar) to be machined, on starting the system rotating.
Some clamping devices with automatic action are of the type known as reversible, i.e. they are capable of providing clamping of the workpiece in the two rotational directions, for example to cut left or right-handed threads, and the present invention concerns more particularly devices of this type.
Automatic clamping devices of the reversible type, comprising several clamping jaws of a generally triangular shape with two serrated or teethed faces, of which one or the other, according to the direction of rotation selected, come into contact with the piece to be clamped, are already known.
In these known devices, each clamping jaw is mounted pivotably about a single pivot carried by an annular rotatable chuck plate and, according to its initial chosen position, it acts with one or the other of its two serrated faces on the piece to be clamped. Although such a device appears simple in principle, its practical realization is complicated and moreover requires the use of very cumbersome jaws, each pivoting about a single pivot relatively remote from the axis of the piece to be machine. A machine thus equipped is therefore relatively complicated, cumbersome and costly.